Diabetes, August 2002

A Night Light Could Keep The Monsters and Diabetic Retinopathy Away

Having a light on at night may do more than keep the monsters away and get you safely to the bathroom.

Research published in The Lancet suggests that normal levels of illumination at night might help prevent diabetic retinopathy, or damage to the retina that could occur in people who have diabetes and which, in extreme cases, can result in blindness.

Uncontrolled Diabetes Leads to a Variety Complications

Uncontrolled diabetes can lead to a number of complications in addition to retinopathy, including kidney problems and even amputation of feet and limbs. All of these complications ultimately result from impaired blood flow, meaning that different areas of the body do not get enough oxygen.

Although this oxygen deprivation no doubt has much to do with the onset of diabetic retinopathy, no one knows exactly why the problem can get so bad in this particular part of the body.

Scientists have speculated that it is because the inner layers of the retina do not get enough oxygen at night. Rods in the eye, which are responsible for night vision, require more oxygen than any cell in the human body at low levels of illumination.

Research has shown that people with diabetes have reduced activity in these deep, inner areas.

This study looked at the effect of oxygen inhalation on retinal function in seven patients with type 2 diabetes. Patients were found to have reduced retinal function before inhaling oxygen and an increase in function of about 31.5 percent after.

"Rods are in the deepest layers of the retina, but our research showed for the first time that the surface layers of the retina, where the retinopathy develops, were subject to hypoxia in people with diabetes after some time in darkness," says Neville Drasdo, study author and a professor in the department of optometry and vision sciences at Cardiff University in the United Kingdom.

If the findings are borne out in future research, there could be major implications for preventing this debilitating disorder.

"The observations shed light on the mechanisms of retinal eye disease in diabetes and suggest the development of retinal damage results, at least in part, from impaired oxygen supply during the dark adaptation at night, a time at which exceptionally high oxygen consumption by the eye rod receptors occurs," says Dr. Fouad Kandeel, director of the department of diabetes, endocrinology, and metabolism at City of Hope National Medical Center in Los Angeles.

"The decrease in oxygen supply is due to the presence of small capillary disease. Thus, reducing the high oxygen demand of retinal tissue through limiting the exposure to darkness may help to retard the development of eye retinal disease in the diabetic patients," Kandeel adds.

Promising News? Not So Fast ...

The jury, though, is still out.

"It has been shown that, depending on the transparency of the closed eyelids, a normal level of illumination (not a night light) would probably be adequate to reduce oxygen consumption by the rods," Drasdo says. "However, we cannot yet advise people to keep lights on throughout the night. The effects of this need further investigation because it might cause some other problems. Research is necessary to determine the best procedure to implement this principle successfully."

Always consult your physician for more information.

Online Resources

(These links are provided for the education and convenience of our Neighbors. AAMC is not responsible for the content of Internet sites.)

American Diabetes Association

Centers for Disease Control and Prevention (CDC)

The Lancet

National Center for Chronic Disease Prevention and Health Promotion

National Heart, Lung, and Blood Institute

National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)

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In Other Diabetes Health News:

American Diabetes Association Sweetens the Snacking

Many persons with diabetes are conditioned to see candy the way vampires view garlic. But patients with a sweet tooth should not automatically shrink from candy or cake.

The American Diabetes Association (ADA) says it is OK for diabetics to eat an occasional piece of pie or a cookie or two, as long as they closely monitor their blood sugar for unhealthy surges. The reason: The kind of carbohydrates diabetics eat is not as important as how much they are eating, according to the group's 2002 nutrition guidelines.

Although diabetes experts have been telling patients for years that modest amounts of sweets are fine, many people with the condition, especially those newly diagnosed, still believe desserts are verboten.

"When they come in, a lot of patients have a lot of misconceptions," says Lara Hassan, a diabetes educator at the Cooper Clinic in Dallas. "They leave happy in the sense that a lot of these misconceptions are clarified."

To be sure, not every person with diabetes can afford to eat all sweets. Some are heavy in saturated fats and loaded with calories—a no-no for many overweight Americans who are developing diabetes in record numbers, Hassan says. On balance, though, most persons with diabetes do not have to make radical changes in their diets as long as they eat prudently.

The recommendations, which appeared in the January issue of Diabetes Care, do not contain much that veers from the ADA's last guidelines, released in 1994. Indeed, Dr. Christopher Saudek, president of the ADA and a diabetes expert at Johns Hopkins University in Baltimore, says what's new about the guidelines is not what's in them but how they were developed.

"We've really tried to distinguish between what lacks evidence and where the evidence is," Saudek says. "We're trying to put some facts into what gets into the hype behind" nutrition therapy for diabetes.

However, the new document does say there is not enough evidence to support a controversial carbohydrate-rating system called the glycemic index, which advocates have insisted is a useful gauge of food's effect on blood glucose.

Instead, the report says, when it comes to affecting blood sugar, a carbohydrate—whether starch, fiber, or sugar—is a carbohydrate is a carbohydrate.

How many carbohydrates a person with diabetes should eat each day varies according to his/her weight, which determines the ideal caloric intake. But typical persons with diabetes should get about half their daily calories in the form of carbohydrates, experts say. Since each gram of sugar, fiber, or starch carries roughly four calories, that works out to about 250 grams for a 2,000 calorie-a-day diet.

To simplify matters, routine servings, such as an apple, an eight-ounce glass of milk, or a slice of bread, contain 15 grams of carbohydrates. So if persons with diabetes are trying to restrict their carbohydrate intake to 1,000 calories a day, they can safely eat 16 servings of these or equivalent foods.

Product labels now print carbohydrate content, so figuring out how many carbohydrates a particular serving holds is easy.

"I'm glad [the ADA is] finally catching up," says Dr. H. Peter Chase, referring to the carbohydrate guidelines. Chase is former director of the Barbara Davis Center for Childhood Diabetes in Denver and a leading blood sugar expert.

Rather than instruct patients, young or old, to eschew carb-rich foods, Chase says he and his colleagues tell them to take a blood glucose test two hours after the snack to make sure they are getting enough insulin. If the answer is no, they should either up their dose of insulin or cut back on the food.

Although very young children might need to receive insulin after their meals, most persons with diabetes should probably be taking the hormone shortly before they eat.

The new ADA guidelines suggest that those with type 2 diabetes and their family members—and everyone else for that matter—get regular physical activity.

Always consult your physician for more information.